442E front suspension help needed - Mazda MX-5 NC

[RTz]

I did what I think is pretty common: The LCA is not adjustable, camber & caster is adjusted with the UCA. I've been happy with that arrangement. Just be aware that shock placement is crucial to allow room for the upper arm to reach the full range of adjustment you intend to make.

[tibimakai]

Thanks for that.
Strut lower mount should be as close as possible to the ball joint, right?
Do you have a straight end plate for the strut mount?
Somewhere I have read, that it weakens the assembly if it's straight. It should have a big radius.
I don't know how true that is, if I recall it correctly, it was in a UK forum.

[RTz]

Strut lower mount should be as close as possible to the ball joint, right?

Yes.

Do you have a straight end plate for the strut mount?
Somewhere I have read, that it weakens the assembly if it's straight. It should have a big radius.
I don't know how true that is, if I recall it correctly, it was in a UK forum.

I used a pre-made bracket with good radius's (similar to the one pictured below). Its welded on and the ball joint is also bolted through the shock bracket. Not that it needs to be, but it makes me warm and fuzzy knowing they are coupled.

[tibimakai]

I was referring to this line:

[tibimakai]

Anybody could confirm my vsusp numbers, if they look OK?
It would be much appreciated.
Today I'm picking up the 1"x.095" DOM tubes.

[tibimakai]

I'm ready to cut the tubes this weekend, but I'm still waiting for somebody to look over my vsusp.
Thank you in advance.

Tibor

[kabuku6]

It'd be easier for people to review your vsup if you posted the current link. You have four or five vsup links on the last page as well, I had to find the most recent.

I think it looks good. At least it looks similar to what I'm aiming for. Really there is no right or wrong answer, it's about preference and what your intended desire is for the car.

https://www.gtplanet.net/forum/threads/ ... 67.385172/

If any of us looked at the vsup for the Camber Car above we'd probably think something was wrong. But it's a remarkable car that did what it was designed for well.

[tibimakai]

Yeah, started talking about other things, and the latest link is a bit back on another page.
Thanks for the confirmation.
The thing is, I have no idea what should I do in vsusp.
The only thing that I worked on, is to keep the roll center as close to the center line as possible and as low as possible.
But I don't know what I'm doing, what should I be looking for.

Latest link:
https://tinyurl.com/Latest-link

[Lonnie-S]

@tibimakai

You can spend a lot of time trying to understand all the various parameters in designing a front suspension, Tibor. In the end, I found I needed to establish a few reasonable values for things and try to work out the best compromise solution that kept the most important ones in reasonable range.

Roll center height is an important one and so is the amount it moves around under the usual motions of the suspension. There are some very good books on suspension design. Some are pretty understandable. If you are building a street car using ordinary tires, things are not as critical as for race cars.

Cheers,

[tibimakai]

Thanks Lonnie.
Basically I have to keep the roll center level low as possible throughout the motion and as close as possible to the center line, right?

[Lonnie-S]

@tibimakai
Right, Tibor, that's one of the major goals.

There are sometimes competing goals too that make our "ideal" setting less desirable. In my case, I became too focused in one design iteration with respect to keeping the front roll center 1" above the ground. In focusing on that too much, I let the effective swing arm length get too short, which has a negative effect on camber control of the suspension in bump and droop. I corrected that in a subsequent iteration and the roll center only moved about 1/4", as I recall.

There is a brief, but relevant discussion of the above issue in Allan Staniforth's book, Competition Car Suspension 4th Edition, at the bottom of page 134. I wouldn't go out and buy the book just for that. I'm just using it as an example of my focusing too much on a specific parameter to the detriment of the overall design.

Also, it's worth remembering that the front and rear suspensions need to work well together to get a good handling vehicle. If you have the most wonderful suspension in the front, and the rear is "just a pig", you're not going to be happy. So, you have to pay attention to the roll center at the rear and how it relates to the front too. Being kind of silly to illustrate the point, what if you have the front roll center at 1" above ground and the rear one at 18"? That's not going to work well.

Paraphrasing Bob Bolles from his book, you want the front and rear suspension trying to do the same thing at the same time. If you have the front suspension working to steer you into a turn and the rear suspension working even harder to steer you out of it, there's going to be trouble.

Cheers,

[tibimakai]

The issue that I have with the rear, is that I'm using the whole rear end(crossmember and all) of the NC MX-5 and I have no idea where the roll center is.
Swing arm length is the FVSA? What would be a good range, right now at ride height is 96.641.
At 3 degree roll angle is 71, at 3" bump is 56.9", 2" droop is 182.
I'm reading a lot on this forum about setting up the suspension, and I have read about camber correction, but I don't know what should look like in a good setup.
Any help is greatly appreciated. I'm ready to cut metal, and I still don't know if I can go with my vsusp numbers or not.

Thanks,

Tibor

[Lonnie-S]

At ~97" for your swing arm length you're in the lower end of the "Long" category according to Staniforth. There's nothing wrong with that, really. You're looking for how the outer wheel behaves in turns, camber changes of both wheels/tires in droop and bump, and toe-in, toe-out on dive and bump and if the roll center is relatively stable. It's very difficult to find a design that is close to "ideal" in all those categories at once.

Sometimes behavior like geometric camber change on droop or bump can be overcome by running a small amount of camber at static ride height. I fussed and fussed with my own design, but found that 1 degree of camber inward at static ride height solved my problem.

I don't know much about Miata's, but given their popularity with racers, I would think technical data on the rear suspension should be available somewhere.

Cheers,

[tibimakai]

This is my latest numbers, what do you think about it?
There is a bunch of info about Miatas, but not about the later generations like the NC.

7 Duratec-Final version-w/3mm wheel spacer

[Lonnie-S]

@tibimakai


I don't use Vsup, Tibor, so I'm no expert. In fact this is the first time I've looked at it in years. It's improved quite a bit visually.

The roll center is very stable laterally and height wise. I did notice that by clicking the little, white round dots on the red and green graphs that camber change is almost 1-1 linear with roll angle. That does surprise me. I would expect it to be fractionally linear, i.e, a fraction of a degree camber change with each degree of roll.

I did a quick look for some information on good targets for camber change, but couldn't find them. I can look tonight and see if I can find them for you.

In pure roll, you'll be most concerned with the camber change on the outside wheel, the one taking most of the weight/force. You'll care about the inside wheel too, but not as much.

I don't know if Vsup does this, but it can be helpful to look at a combination of roll and dive as well just to make sure you don't get a lot of toe movement and camber change with that combination like when braking and steering into a corner.